Photochromic naphthopyran compounds

ABSTRACT

A naphthopyran compound of general formula (I) ##STR1## wherein R 1  represents a group of the formula --NR 2  R 3  wherein each of R 2  and R 3 , which may be the same or different, independently represents an alkyl group, or a carbocyclic or heterocyclic group, or R 2  and R 3  taken together with the nitrogen atom to which they are attached represent a heterocyclic ring having one or more hetero atoms and which may optionally carry at least one substituent selected from alkyl, aryl, or heteroaryl groups; each of R 4  and R 5 , which may be the same or different, independently represents an alkyl, alkenyl, carbocyclic or heterocyclic group, or R 4  and R 5  taken together with the carbon atom to which they are attached form a carboxylcyclic ring or a heterocyclic ring; and R 6  represents a hydrogen atom or a substituent selected from alkyl, alkoxy, aryl, aryloxy, heteroaryl, halogen, a group of formula R 1  as defined above, azo, imino, amide, carboxylate, ester, cyano, trifluoromethyl or nitro, and in addition R 6  may represent a carbocyclic or heterocyclic ring fused to ring A. The naphthopyran compounds of the invention are useful as photochromic materials in lenses, e.g. sunglasses, and photochromic transparencies for cars and aircraft. The invention also provides, as new intermediate compounds, amine-substituted chloro-naphthols and amine-substituted naphthols.

This application is a 371 of PCT/GB94/00628 filed Mar. 25, 1994.

The present invention relates to certain novel photochromic naphthopyrancompounds, and to articles and compositions containing them.

Photochromism is a well-known physical phenomenon which is observed withcertain classes of chemical compounds. A detailed discussion of thisphenomenon can be found in "Photochromism: Molecules and Systems",Studies in Organic Chemistry 40, Edited by H. Durr and H. Bouas-Laurent,Elsevier 1990.

Naphthopyran compounds as a class of compounds are known to be capableof exhibiting a photochromic effect. For example, U.S. Pat. No.4,980,089 describes a series of photochromic naphthospiropyran compoundscontaining a norcamphor group or a tricyclodecane group at the2-position of the naphthospiropyran ring (This 2-position corresponds tothe 3-position of the ring in the numbering system used in the presentspecification).

A series of novel reversible photochromic naphthopyran compoundscarrying an acetoxy group (or analogues thereof) at the 5-position ofthe naphthopyran ring is described in WO 92/09503.

U.S. Pat. No. 5,106,998 describes a variety of photochromic compoundsincluding various naphthopyran compounds of different structures.

U.S. Pat. No. 5,066,818 describes a group of novel reversiblephotochromic naphthopyran compounds having at least oneortho-substituted phenyl group at the 3-position of the pyran ring.

We have now found a group of naphthopyran compounds which providesubstantially greater induced optical density in their darkened statethan other known naphthopyran compounds. The common characteristic ofthe novel naphthopyran compounds of the present invention is that theycarry a substituted amino group in the 6-position of the molecule.

Accordingly, the present invention provides a naphthopyran compound ofgeneral formula (I) ##STR2## wherein R₁ represents a group of theformula --NR₂ R₃ wherein each of R₂ and R₃, which may be the same ordifferent, independently represents an alkyl group, or a carbocyclicgroup, preferably aryl, or a heterocyclic group, or R₂ and R₃ takentogether with the nitrogen atom to which they are attached represent aheterocyclic ring having one or more hetero atoms and which mayoptionally carry at least one substituent selected from alkyl, aryl orheteroaryl groups;

each of R₄ and R₅, which may be the same or different, independentlyrepresents an alkyl, alkenyl, carbocyclic or heterocyclic group, or R₄and R₅ taken together with the carbon atom to which they are attachedform a carbocyclic ring or a heterocyclic ring; and

R₆ represents a hydrogen atom or a substituent selected from alkyl,alkoxy, aryl, aryloxy, heteroaryl, halogen, a group of formula R₁ asdefined above, azo, imino, amide, carboxylate, ester, cyano,trifluoromethyl or nitro, and in addition R₆ may represent a carbocyclicor heterocyclic ring fused to ring A.

Throughout this specification, unless stated otherwise, the term "alkyl"is to be taken to mean an alkyl group having from 1 to 4 carbon atoms.Similarly, the term "alkoxy" is to be taken to mean an alkoxy grouphaving from 1 to 4 carbon atoms.

Furthermore, in the definitions of R₁, R₄, R₅ and R₆ above, wheneverreference has been made to a carbocyclic or heterocyclic ring (orgroup), unless specified otherwise it is to be understood that suchcarbocyclic or heterocyclic rings (or groups) may be unsubstituted ormay carry one or more substituents chosen from halogen atoms, alkyl,alkoxy, aryl, aryloxy, heteroaryl, amino, a group --NR₂ R₃ as definedabove, azo, imino, amide, carboxylate, ester, cyano, trifluoromethyl ornitro groups, or, further, such rings may have one or more further ringswhich are fused thereto.

For the avoidance of doubt, in the definition of R₁ above, the group--NR₂ R₃ includes within its scope ring systems in which one or morefurther rings are fused to the heterocyclic ring, and such ring systemsmay incorporate saturated and/or unsaturated rings. Typical examples ofsuch --NR₂ R₃ groups include a tetrahydroisoquinoline substituent offormula: ##STR3## or an indoline substituent of formula ##STR4## or ahexahydrocarbazole substituent of formula ##STR5##

In the compounds of formula (I), ring A may carry more than onesubstituent R₆.

In a group of preferred compounds in accordance with the invention, theR₁ substituent is a piperidino group, a morpholino group or an N-methylpiperazino group.

Preferably, the substituents R₄ and R₅ on the pyran ring are chosen froma phenyl group, a 4-trifluoromethyl -phenyl group, a 4-alkoxyphenylgroup (preferably 4-methoxyphenyl), a 2,4-di(alkoxy)phenyl group(preferably 2,4-dimethoxyphenyl) or a 4-dialkylamino-phenyl group(preferably 4-dimethylamino-phenyl).

Alternatively, the R₄ and R₅ substituents together with the carbon atomto which they are attached form a spiro-indoline group carrying alkyl oraryl substituents or alicyclic C₁₋₁₈ groups at the 1-, 3-, 3-positionsof the indoline ring. The alkyl groups may be linear or branched, andmay have up to 18 carbon atoms. If desired, the aromatic ring of theindoline group may carry one or more substituents which are substituentsas defined for R₆ above.

It is also envisaged that the advantageous properties of the compoundsof the present invention will be obtained with a compound of generalformula (I) in which the R₄ and R₅ substituents together with the carbonatom to which they are attached form a spiro-adamantylidene group.

The naphthopyran compounds of the present invention may be prepared by ageneral preparative method which is based on the following reactionscheme: ##STR6##

The compounds of formula (I) in which R₄ and R₅ taken together representa spiro-indoline group are made by a slightly different synthetic route,as shown in the following reaction scheme: ##STR7##

Accordingly, the present invention also provides a process for preparinga naphthopyran compound of general formula (I) as defined above, whichprocess comprises

(a) chlorinating a solution of a 2-naphthol of general formula (VI):##STR8## wherein R₆ is as defined above, in an organic solvent toproduce the corresponding 1,1-dichloronaphth-2-one which is reacted withan amine of general formula R₁ H in the presence of an organic base(typically, a tertiary amine such as triethylamine) to generate achloro-naphthol of general formula (III): ##STR9## (b) subjecting thechloro-naphthol of general formula (III) to a hydrodehalogenationreaction to produce a substituted naphthol of general formula (IV):##STR10## and then either: (c) condensing the substituted naphthol ofgeneral formula (IV) with a propargyl alcohol of general formula (V):##STR11## wherein R₄ and R₅ are as defined above, in the presence ofacidic alumina, trifluoroacetic acid or another like acidic catalyst, or

(c') when R₄ and R₅ together with the carbon atom to which they areattached form a spiro-indoline group, condensing the substitutednaphthol of general formula (IV) with a 2-alkylidene indole of generalformula (IX): ##STR12## wherein R₇ represents an alkyl group or an arylgroup or an alicyclic C₁₋₁₈ group, in the presence of a trialkylorthoformate.

In the preparation processes described above,1,1-dichloronaphth-2-one(II) is first prepared from 2-naphthol(VI) by amethod derived from the process described by G. M. Iskander et. al. inJ. Chem. Soc. (C), 1970, 1701-1703.

Thus, 1,1-dichloronaphth-2-one (II) is produced in good yield from thedirect chlorination of 2-naphthol. The chlorination is carried out byvigorously bubbling chlorine through a stirred naphthol solution in asolvent such as chloroform, carbon tetrachloride, benzene, diethyl etheror toluene, at room temperature, at a relatively fast rate (e.g. 2-3g/min for a 0.1 mol scale reaction) until a two-fold excess of chlorinehas been added. The use of a two-fold excess of chlorine is important inso far that yields are kept high and the production of unwantedby-products is kept to a minimum thereby avoiding the need for isolationand purification of the dichloro compound (II) after this particularstep. On completion of the chlorination, nitrogen is bubbled through thestirred solution at a fast rate in order to drive off any excesschlorine and also to clear the solution of hydrogen chloride producedduring the reaction. Hydrogen chloride is known to react with the1,1-dichloronaphthone at elevated temperatures thereby causing a yieldreduction. The majority of the HCl is driven off during the reaction.

We have discovered that the dichloro compound (II) is extremely labileto attack at the 4-position by amines resulting in the formation of4-amine-substituted 1-chloro-2-naphthols of formula (III) and HCl, thelatter being removed by filtration as a tertiary amine/HCl salt (e.g.triethylamine hydrochloride).

In general, the 4-amine-substituted compounds of formula (III) areprepared by first adding a molar excess of an organic base such astriethylamine in one portion to the solution of the dichloro compound(II) followed by the controlled addition of a slight excess (e.g. 10%)of secondary amine of formula R₁ H (e.g. piperidine), whilst maintainingthe overall reaction temperature below 25° C. The resulting mixture isfiltered to remove any precipitated amine/HCl salt and the filtratewashed with water to remove any remaining salt and the dried filtrateevaporated to yield the chloroaminonaphthol of formula (III).

The hydro-dehalogenation of the aminochloronaphthols of formula (III) togenerate the 4-amino-2-naphthols of formula (IV) can be carried outusing a number of well-known reagents and conditions (e.g. Raney-Nickel)but the preferred method is by catalytic medium-pressure hydrogenationunder basic conditions, for example aqueous KOH or NaOH. A typicalcatalyst is 5% Pd on charcoal. The hydro-dehalogenation step may becarried out on relatively impure aminochloronaphthols but impurities maypoison the catalyst thereby reducing the yields. The 4-amino-2-naphtholcompounds of formula (IV) are formed in moderate to good yields.

The synthesis of naphthopyran compounds from naphthols is generally wellknown and is described in detail, for example, by L. Merlini in Advancesin Heterocyclic Chemistry, 1975, 18, 159 and in a number of patents, forexample, U.S. Pat. No. 5,066,818, U.S. Pat. No. 4,990,287, U.S. Pat. No.4,980,089 and WO 92/09593. Typically, in the process of the presentinvention, the formation of the 3,3-disubstituted and3-spiro-carbocyclic naphthopyrans takes place via an initialcondensation/etherification reaction between an amino-naphthol ofgeneral formula (IV) and a propargyl alcohol of general formula (V) inthe presence of acidic alumina (e.g. Brockmann 1 alumina),trifluoroacetic acid or other like acidic catalyst.

Compounds of the general formula (I) having a spiro-indoline substituentat position 3 (e.g. compound (X) in Scheme B) are made by a differentsynthetic route as illustrated in Scheme B above. The preparation ofthese materials can be performed by a one-pot reaction in which anamino-naphthol of general formula (IV) is reacted with a2-alkylideneindote of general formula (IX) in the presence of atrialkylorthoformate, e.g. triethylorthoformate. The general mechanismand synthesis of such spiroheterocyclo-naphthopyrans is described morefully by H. Durr and H. Bouas-Laurent in Studies in Organic Chemistry40; Photochromism:Molecules and Systems, Elsevier 1990, chapter 8,419-451.

The novel naphthopyran compounds of the present invention are found tobe particularly useful as photochromic materials to be incorporated intopolymeric host materials so as to impart photochromic properties to thesaid polymeric host materials.

The photochromic naphthopyran compounds of the present invention areincorporated into the plastics host material in known manner, forexample as described in European Patent No. 0245020 or U.S. Pat. No.5,066,818.

The naphthopyran compounds of the invention exhibit substantiallygreater induced optical density (IOD) than prior art materials ofcomparable structure. As a result, the amount of photochromic materialrequired to impart a useful degree of photochromism to a polymeric hostmaterial or to a solution is greatly reduced when compared to the amountrequired to obtain an equivalent photochromic effect with prior artphotochromic materials.

The use of reduced quantities of the photochromic materials of theinvention not only gives a saving in cost, but also has the addedadvantage that there is a consequent reduction in any undesirable colourthat the photochromic materials may impart in the bleached state, eitherby way of the inherent colour of the photochromic material itself, or byway of any coloured degradation/fatigue products that may be generatedduring use of the photochromic material.

A further advantage of the photochromic naphthopyran materials of thepresent invention is that they exhibit a fatigue performance which is asgood as, if not better than, known photochromic compounds of similarstructure.

The colour range of the naphthopyrans of the present invention is 400 to550 nm; thus, the materials of the present invention impart a yellow ororange or red or red-purple colouration in their darkened state. In thefaded or bleached condition the materials exhibit a colourless or palecolouration.

Typical polymeric host materials are optically clear polymer materials,such as polymers of polyol(allyl carbonate)-monomers, polyacrylates suchas polymethylmethacrylates, cellulose acetate, cellulose triacetate,cellulose acetate propionate, cellulose acetate butyrate, poly(vinylacetate), poly(vinyl alcohol), polyurethanes, polycarbonates,polyethylene terephthalate, polystyrene, styrene/methylmethacrylatecopolymers, styrene/acrylonitrile copolymers, and polyvinylbutyral.Transparent copolymers and blends of the transparent polymers are alsosuitable as host materials. Polymers of the type described in EP 0453149are also suitable.

Preferably, the polymeric host material is an optically clearpolymerized organic material such as a polymer of triethylene glycoldimethacrylate (TEGDM) or a polymer of diethylene glycol bis(allylcarbonate) (sold under the trade name CR-39), or SPECTRALITE--a materialsold by Sola Optical USA.

Usually, the amount of photochromic naphthopyran compound incorporatedin the polymeric host material ranges from 0.001 to 0.1 wt %, based onthe weight of the polymeric host material.

In some applications, it may be desirable or advantageous to combine thenaphthopyran compounds of the present invention with other photochromicmaterials to obtain an aggregate colour effect. For example,spiro-oxazine materials may have a colour range of 530 to 680 nm whichmeans that in the darkened condition the spiro-oxazines impart ared-purple or purple or blue or blue-green or green colouration to ahost material. Thus, the present naphthopyran compounds arecomplementary to known spiro-oxazine materials such as those describedin our European Patent No. 0245020, or in our UK Patent ApplicationsNos. 92/25346, 92/25347 and 92/25348, or to the spiro (indolino)naphthoxazines, spiro (indolino) pyrido benzoxazines and spiro(indolino) benzoxazines described in U.S. Pat. Nos. 4,637,698,3,562,172, 3,578,602, 4,816,584, 4,215,010 and 4,342,668, and can becombined with such other photochromic materials.

Typically, when used in combination, the further additional photochromicmaterial is present in an amount of from 0.001 to 0.5 weight % based onthe weight of the polymeric host material.

Examples of suitable uses of the photochromic plastic articlesincorporating the naphthopyran compounds of the invention are in themanufacture of plano lenses, e.g. for sunglasses, and ophthalmic lensesand as photochromic transparencies for vehicles such as cars andaircraft.

Some of the intermediate compounds used to prepare the naphthopyrancompounds of the invention are themselves new compounds.

According to a further aspect of the present invention there is provideda chloro-naphthol compound of general formula (III): ##STR13## whereinR₁ and R₆ are as defined above.

According to a still further aspect of the present invention there isprovided a naphthol compound of general formula (IV) ##STR14## whereinR₁ and R₆ are as defined above, with the proviso that R₁ is not--N(CH₃)₂.

The preparation of these intermediate compounds has been described abovein general terms in the description of the processes for preparing thenaphthopyran compounds of general formula (I) with reference to SchemeA, and more detailed preparative methods of these intermediates aregiven in the following Examples.

The following Examples illustrate the present invention.

EXAMPLE 1

3,3-Dianisyl-6-piperidino-3H-naphtho[2,1-b]pyran.

(a) 1-Chloro-4-piperidino-2-naphthol

2-Naphthol (28.8 g; 0.200 mol) was dissolved in toluene (210 ml) bywarming. The pale brown solution was cooled and vigorously stirred untilthe naphthol began to precipitate and chlorine (30.20 g;0.425 mol) wasthen passed through the solution at approximately 2.5-3.0 g/min followedimmediately by nitrogen gas. The resulting amber solution was treatedfirstly with triethylamine (24.68 g;0.244 mol) in one portion and thenwith a solution of piperidine (19.55 g;0.230 mol), in toluene (210 ml),dropwise over 1.5 hours keeping the temperature at 15°-20° C. Theresulting brown mixture was filtered to remove triethylaminehydrochloride as a white amorphous solid. The toluene filtrate waswashed in water, dried and evaporated to give1-chloro-4-piperidino-2-naphthol (of structure 3a below) as a brownviscous oil (61.80 g;77% purity by gel permeation chromatography;91%yield based on 2-naphthol). Distillation gave the naphthol as a viscousamber gum B.Pt 150° C./0.3 mmHg. ##STR15## (b) 4-Piperidino-2-naphthol

1-Chloro-4-piperidino-2-naphthol (3.0 g;0.0115 mol), prepared as in 1(a)above, dissolved in 1.25M aqueous NaOH (100 ml) was stirred and heatedto 75°-80° C. To the solution was added (50/50) Raney Nickel (14.0 g)portionwise over 1 hour. The mixture was stirred for 1.5 h, cooled thenfiltered through celite with washing (3×2M NaOH). The filtrate wasneutralised with conc. HCl and extracted into CH₂ Cl₂, dried andevaporated to yield crude 4-piperidino-2-naphthol (1.46 g;56%) as ared-orange oil. Purification by flash chromatography over silica (CH₂Cl₂) gave 4-piperidino-2-naphthol (of structure 4a below) as a red oil.##STR16## (c) A mixture of 4-piperidino-2-naphthol (1.00 g; 0.0044 mol), prepared as described in 1(b) above, 1,1-dianisylprop-2-yn-1-ol(1.18g;0.0044 mol), acidic alumina Brockmann 1 (4 g) and toluene (40.0 ml)was heated and stirred for 1.5 h, cooled and filtered. The filtrate waswashed with 2M NaOH then water, dried and evaporated to give a red gum.Purification of the gum by flash chromatography over silica (20%ethylacetate in hexane) affored an orange gum which upon triturationwith pet. ether (40-60)/diethyl ether yielded 3,3-dianisyl-6-piperidino-3H-naphtho[2,1-b]pyran (of structure 5a below) as an off-white solid(5% yield), m.pt. 114°-119° C. ##STR17##

EXAMPLE 2

1,3,3-Trimethyl-6'-morpholinospiro[indoline-2,3'-[3H]-naphtho[2,1-b]pyran].

(a) 1-Chloro-4-morpholino-2-naphthol

2-Naphthol (28.8 g; 0.200 mol) was dissolved in toluene (200 ml) bywarming. The pale brown solution was cooled and vigorously stirred untilthe naphthol began to precipitate and chlorine (31.29 g;0.442 mol) wasthen passed through the solution at approximately 2.5-3.0 g/min followedimmediately by nitrogen gas. The resulting amber solution was treatedfirstly with triethylamine (24.68 g;0.244 mol) in one portion and thenwith a solution of morpholine (17.40 g;0.20 mol) in toluene (180 ml)dropwise over 1.5 hours keeping the temperature at 15°-20° C. Theresulting brown mixture was filtered to remove triethylaminehydrochloride as a white amorphous solid. The toluene filtrate waswashed with water, dried and evaporated to give1-chloro-4-morpholino-2-naphthol as a brown viscous oil (57.76 g).Purification by chromatography over silica (eluent: 15% ethyl acetate intoluene) gave the product as an off-white solid (34.37 g;65%). Furtherpurification by crystallisation from toluene gave the product as a whitesolid, m.pt. 163°-65° C. ##STR18## (b) 4-Morpholino-2-naphthol

1-Chloro-4-morpholino-2-naphthol (15.0 g;0.057 mol), prepared asdescribed in 2(a) above, was dissolved in 10% aqueous potassiumhydroxide (100 ml) and was treated in the presence of palladium oncharcoal (1.75 g;5%) at room temperature under 3 atmospheres of hydrogenuntil a stoichiometric amount of hydrogen was absorbed (approximately24h). The palladium catalyst was removed by filtration and the filtrateneutralised with glacial acetic acid to afford 4-morpholino-2-naphtholas a white solid (8.5 g;65%), m.pt. 231°-232° C. ##STR19##

(c) A mixture of 4-morpholino-2-naphthol (0.47 g;0.002 mol), prepared asin 2(b) above, 1,3,3-trimethyl-2-methyleneindole (0.8 g;0.0022 mol) andtriethylorthoformate (10.0 ml) was stirred under nitrogen and heated toreflux for 18 hrs. The resulting purple solution was cooled andevaporated to remove the excess triethylorthoformate and the residueflash chromatographed over silica (40% diethyl ether in hexane) to yieldan orange gum (0.28 g; yield 34%). Trituration of the gum with diethylether afforded the 1,3,3-trimethyl-6'-morpholinospiro[indoline-2,3'-[3H]-naphtho[2,1-b]pyran having the structure shown belowas a pale brown solid, m.pt 191°-194° C. ##STR20##

EXAMPLE 3

3,3-Dianisyl-6-morpholino-3H-naphtho[2, 1-b]pyran

4-Morpholino-2-naphthol was prepared as described in Example 2(b). Amixture of 4-morpholino-2-naphthol (0.50 g;0.0022 mol),1,1-dianisylprop-2-yn-1-ol (0.59 g; 0.0022 mol), acidic aluminaBrockmann 1(4 g) and toluene (35.0 ml) was heated and stirred for 1.5 h,cooled, filtered and the solid washed with toluene. The filtrate wasevaporated to give an orange crystalline solid which was washed withdiethyl ether to give 3,3-dianisyl -6-morpholino-3H-naphtho[2,1-b]pyranas a white solid (0.61 g;58% yield), m.pt. 211°-213° C. ##STR21##

EXAMPLE 4

3-Anisyl-3-(4-trifluoromethyl)phenyl-6-morpholino-3H-naphtho[2,1-b]pyran.

4-Morpholino-2-naphthol was prepared as described in Example 2(b). Amixture of 4-morpholino-2-naphthol (0.23 g;0.001 mol),1-anisyl-1-(4-trifluoromethyl) phenylprop-2-yn-1-ol (0.29 g;0.001 mol),acidic alumina Brockmann 1 (3 g) and toluene (40.0 ml) was heated andstirred for 1.5 h, cooled, filtered and the solid washed with toluene.The filtrate was evaporated to give a pale orange crystalline solidwhich was washed with diethyl ether to give3-anisyl-3-(4-trifluoromethyl)phenyl-6-morpholino-3H-naphtho[2,1-b]pyran as a white solid (0.12 g;24%yield), m.pt. 226°-228° C. ##STR22##

EXAMPLE 5

3-Anisyl-3-(2,4-dimethoxyphenyl)6-morpholino-3H-naphtho [2,1-b]pyran.

4-Morpholino-2-naphthol was prepared as described in Example 2(b). Amixture of 4-morpholino-2-naphthol (0.25 g;0.0011 mol),1-anisyl-1-(2,4-dimethoxy) phenylprop-2-yn-1-ol (0.33 g;0.0011 mol),acidic alumina Brockmann 1(3 g) and toluene (40.0 ml) was heated andstirred for 1.5 h, cooled, filtered and the solid washed with toluene.The filtrate was evaporated and chromatographed over silica (eluent: 40%ethylacetate in hexane) to give a dark brown gum which was washed withpet. ether (30-40) to give 3-anisyl-3-(2,4-dimethoxy)phenyl-6-morpholino -3H-naphtho[2,1-b]pyran as a white solid (0.10 g;18%yield), m.pt. 163°-165° C. ##STR23##

For the purposes of comparison a number of corresponding compoundshaving no substitution at the 6-position were also prepared. Thepreparation of these compounds is described in the following ComparativeExamples.

COMPARATIVE EXAMPLE 1

3,3-Dianisyl-3H-naphtho[2,1-b]pyran.

A mixture of 2-naphthol (3.23 g;0.0224 mol), 1,1-dianisylprop-2-yn-1-ol(6.00 g;0.0224 mol), acidic alumina Brockmann 1(6 g) and toluene (250ml) was heated and stirred for 1.5 h, cooled, filtered and the solidwashed with toluene. The filtrate was evaporated to give a pale purpletacky solid which was washed with pet. ether (40-60)/diethyl ether toyield crude product (7.07 g). Purification of the solid bycrystallisation from ethylacetate gave3,3-dianisyl-3H-naphtho[2,1-b]pyran as a white solid (5.52 g;66% yield),m.pt 176°-177° C. ##STR24##

COMPARATIVE EXAMPLE 2

3-Anisyl-3-(p-trifluoromethyl)phenyl-3H-naphtho[2,1-b]pyran.

A mixture of 2-naphthol (1.44 g;0.010 mol),1-anisyl-1-(4-trifluoromethyl)phenylprop-2-yn-1-ol (3.22 g;0.0105 mol),acidic alumina Brockmann 1 (8 g) and benzene (40.0 ml) was heated andstirred for 3 h, cooled, filtered and the solid washed with toluene. Thefiltrate was evaporated to give an orange oil which was chromatographedover silica (eluent: 10% ethylacetate in pet. ether (40-60)) to give apale yellow oil which solidified on trituration with diethyl ether toyield 3-anisyl-3-(4-trifluoromethyl)phenyl -3H-naphtho[2,1-b]pyran as awhite solid (1.60 g;37% yield), m.pt. 136°-137.5° C. ##STR25##

COMPARATIVE EXAMPLE 3

3-Anisyl-3-(2,4-dimethoxyphenyl)-3H-naphtho[2,1-b]pyran.

A mixture of 2-naphthol (0.48 g;0.00335 mol),1-anisyl-1-(2,4-dimethoxy)phenylprop-2-yn-1-ol (1.00 g; 0.00335 mol),acidic alumina Brockmann 1 (2 g) and toluene (40.0 ml) was heated andstirred for 2 h, cooled, filtered and the solid washed with toluene. Thefiltrate was evaporated and chromatographed over silica (eluent; 20%ethylacetate in hexane) to give an orange oil which was washed with pet.ether (60-80)/diethyl ether to give the crude product as an off-whitesolid which was crystallised from ethylacetate/hexane to give3-anisyl-3-(2,4-dimethoxy) phenyl-3H-naphtho[2,1-b]pyran as a whitesolid (0.77 g;56% yield), m.pt. 140°-143° C. ##STR26##

The photochromic properties of the naphthopyran compounds of the presentinvention were tested by preparing, in conventional manner, by a directcasting process, 2.4 mm plates of a U.V. curable plastics host material(made and sold as SPECTRALITE by Sola Optical USA) incorporating thephotochromic naphthopyran in a concentration of 0.05% w/w.

Similar plates were made with samples of the comparative compounds.

The resultant plates were illuminated under standard solar simulationconditions at Air Mass 2 at 21° C. (see Parry Moon, J. Franklin Inst.230, (1940), p 583-617). The measurements which were made on the samplesin the darkened condition were taken when the samples had reached asteady state; this steady state was deemed to have been reached after 10minutes in the darkened condition.

The results obtained are shown in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                Bleached                                                                             Darkened    IOD     λ max                                       IVT    IVT         λ max                                                                          nm                                         ______________________________________                                        Examples                                                                      1         86.1     58.3        1.95  452                                      3         87.4     58.4        1.57  452                                      4         90.4     75.4        1.72  432                                      5         79.5     48          2.39  432                                      Comparative                                                                   Examples                                                                      1         91.2     79.9        0.12  490                                      2         91.2     84.0        0.15  450                                      3         89.9     54.8        0.69  488                                      ______________________________________                                    

The results in Table 1 show the integrated visible transmission (IVT)measured in both the bleached condition and the darkened condition.These values show, for each material, the typical visual photochromicrange which can be achieved.

These IVT values enable one to calculate the induced optical density atthe point of maximum adsorption of the chromophore (IOD at λ max) bymeans of the following relationship: ##EQU1##

The results obtained are set out in Table 1. The relatively high IODvalues obtained with the naphthopyran compounds of the present invention(ranging from 1.57 to 2.39) demonstrate the very dense colouring whichis obtained with the photochromic materials of the present invention.These results contrast markedly with the low IOD values obtained withthe comparative samples (ranging from 0.12 to 0.69).

The photochromic naphthopyran compounds of the present invention arealso found to exhibit very good fatigue resistance, that is to say thatthe naphthopyran compounds of the present invention are found, ingeneral, to be capable of maintaining their good photochromic propertiesand intense dark colouration in the darkened state over relatively longperiods of time without undergoing any substantial degree ofdegradation.

In addition to the intermediates described in Examples 1(a), 1(b) and2(a) and 2(b), the following intermediate compounds were also prepared:

EXAMPLE 6

(a) 1-Chloro-4-pyrrolidino-2-naphthol

2-Naphthol (14.43 g; 0.100 mol) was dissolved in toluene (200 ml) bywarming. The pale brown solution was cooled and vigorously stirred untilthe naphthol began to precipitate and chlorine (15.22 g;0.21 mol) wasthen passed through the solution at approximately 2.5-3.0 g/min followedimmediately by nitrogen gas. The resulting amber solution was treatedfirstly with triethylamine (12.12 g;0.12 mol) in one portion and thenwith a solution of pyrrolidine (7.10;0.10 mol), in toluene (100 ml),dropwise over 1.5 hours keeping the temperature at 15°-20° C. Theresulting brown mixture was filtered to remove triethylaminehydrochloride as a white amorphous solid. The toluene filtrate waswashed with water, dried and evaporated to give1-chloro-4-pyrrolidino-2-naphthol as a brown viscous oil (25.87 g).Purification by chromatography over silica (eluent: toluene) gave theproduct as a red-brown oil (3.825 g;15%). ##STR27## (b)4-Pyrrolidino-2-naphthol

1-Chloro-4-pyrrolidino-2-naphthol (2.47 g;0.010 mol), prepared asdescribed in Example 6(a), was dissolved in 10% aqueous potassiumhydroxide (50 ml) and was treated in the presence of palladium oncharcoal (1.00 g;5%) at room temperature under 3 atmospheres of hydrogenuntil a stoichiometric amount of hydrogen was absorbed (approximately24h). The palladium catalyst was removed by filtration and the filtrateneutralised with glacial acetic acid. The solution was extracted withdichloromethane (2×50 ml), the extracts combined, dried and evaporatedto afford crude 4-pyrrolidino-2-naphthol as an unstable dark oil (0.58g;27%). The crude product could not be purified further usingconventional methods. ##STR28##

EXAMPLE 7

(a) 1-Chloro-4-indolino-2-naphthol

2-Naphthol (28.8 g; 0.200 mol) was dissolved in toluene (200 ml) bywarming. The pale brown solution was cooled and vigorously stirred untilthe naphthol began to precipitate and chlorine (30.21 g;0.43 mol) wasthen passed through the solution at approximately 2.5-3.0 g/min followedimmediately by nitrogen gas. The resulting amber solution was treatedfirstly with triethylamine (24.68 g;0.244 mol) in one portion and thenwith a solution of indoline (23.8 g;0.20 mol) , in toluene (200 ml) ,dropwise over 1.5 hours keeping the temperature at 15°-20° C. Theresulting brown mixture was filtered to remove triethylaminehydrochloride as a white amorphous solid. The toluene filtrate waswashed with water, dried and evaporated to give1-chloro-4-indolino-2-naphthol as a brown viscous oil (69.7 g).Purification by chromatography over silica (eluent: 15% dichloromethanein toluene) gave the product as a brown-green oil (43.2 g;73%). Furtherpurification by distillation (170° C./0.1 mmHg) gave the naphthol as apale brown viscous gum. ##STR29## (b) 4-Indolino-2-naphthol

1-Chloro-4-indolino-2-naphthol (5.6 g;0.019 mol), purified as describedin Example 7(a), was dissolved in 10% aqueous potassium hydroxide (100ml) and was treated in the presence of palladium on charcoal (1.75 g;5%)at room temperature under 3 atmospheres of hydrogen until astoichiometric amount of hydrogen was absorbed (approximately 24h). Thepalladium catalyst was removed by filtration and the filtrateneutralised with glacial acetic acid. The solution was extracted withdichloromethane (2×50 ml), the extracts combined, dried and evaporatedto afford 4-indolino-2-naphthol (3.4 g;69%) as a red-orange oil.##STR30##

We claim:
 1. A naphthopyran compound of general formula (I)wherein R₁represents a group of the formula --NR₂ R₃ wherein each of R₂ and R₃,which may be the same or different, independently represents an alkylgroup, or a carbocyclic or heterocyclic group, or R₂ and R₃ takentogether with the nitrogen atom to which they are attached represent aheterocyclic ring having one or more hetero atoms and which mayoptionally carry at least one substituent selected from alkyl, aryl orheteroaryl groups; each of R₄ and R₅, which may be the same ordifferent, independently represents an alkyl, alkenyl, carbocyclic orheterocyclic group, or R₄ and R₅ taken together with the carbon atom towhich they are attached form a carbocyclic ring or a heterocyclic ring;and R₆ represents a hydrogen atom or a substituent selected from alkyl,alkoxy, aryl, aryloxy, heteroaryl, halogen, a group of formula R₁ asdefined above, azo, imino, amide, carboxylate, ester, cyano,trifluromethyl or nitro, and in addition R₆ may represent a carbocyclicor heterocyclic ring fused to ring A.
 2. A naphthopyran compoundaccording to claim 1, wherein the R₁ substituent is a piperidino group.3. A naphthopyran compound according to claim 1, wherein the R₁substituent is a morpholino group.
 4. A naphthopyran compound accordingto claim 1, wherein the R₄ and R₅ substituents are chosen from a phenylgroup, a 4-trifluoromethylphenyl group, a 4-alkoxyphenyl group, a2,4-di(alkoxy)phenyl group or a 4-dialkylaminophenyl group.
 5. Anaphthopyran compound according to claim 4, wherein the R₄ and R₅substituents are chosen from a 4-methoxyphenyl group, a2,4-dimethoxyphenyl group or a 4-dimethylaminophenyl group.
 6. Anaphthopyran compound according to claim 1, wherein the R₄ and R₅substituents together with the carbon atom to which they are attachedform a spiro-indoline group carrying alkyl or aryl substituents oralicyclic C₁₋₁₈ groups at the 1-, 3-, 3-positions of the indoline ring.7. A naphthopyran compound according to claim 6, wherein the said alkylgroups are linear or branched C₁₋₁₈ groups.
 8. A naphthopyran compoundaccording to claim 6, wherein the aromatic ring of the indoline carriesone or more substituents which are substituents as defined for R₆ inclaim
 1. 9. A process for preparing a naphthopyran compound of generalformula (I) as defined in claim 1, which process comprises(a)chlorinating a solution of a 2-naphthol of general formula (VI):##STR31## wherein R₆ is as defined in claim 1, in an organic solvent toproduce the corresponding 1,1-dichloronaphth-2-one which is reacted withan amine of general formula R₁ H in the presence of an organic base togenerate a chloro-naphthol of general formula (III): ##STR32## (b)subjecting the chloro-naphthol of general formula (III) to ahydrodehalogenation reaction to produce a substituted naphthol ofgeneral formula (IV): ##STR33## and then either: (c) condensing thesubstituted naphthol of general formula (IV) with a propargyl alcohol ofgeneral formula (V): ##STR34## wherein R₄ and R₅ are as defined in claim1, in the presence of acidic alumina, trifluoroacetic acid or anotherlike acidic catalyst, or (c') when R₄ and R₅ together with the carbonatom to which they are attached form a spiro-indoline group, condensingthe substituted naphthol of general formula (IV) with a 2-alkylideneindole of general formula (IX): ##STR35## wherein R₇ represents an alkylgroup or an aryl group or an alicyclic C₁₋₁₈ group, in the presence of atrialkyl orthoformate.
 10. A photochromic article comprising a polymerichost material having a naphthopyran compound as defined in claim 1incorporated therein or applied thereto.
 11. A photochromic articleaccording to claim 10, wherein the polymeric host material is selectedfrom polymers of polyol (allyl carbonate) monomers, polyacrylates,poly(alkylacrylates), cellulose acetate, cellulose triacetate, celluloseacetate propionate, cellulose acetate butyrate, poly(vinyl acetate),poly(vinyl alcohol), polyurethanes, polycarbonates, polyethyleneterephthalate, polystyrene, styrene/methylmethacrylate copolymers,styrene/acrylonitrile copolymers, and polyvinylbutyral.
 12. Aphotochromic article according to claim 11, wherein the polymeric hostmaterial is a polymer of triethyleneglycol dimethacrylate (TEGDM), or apolymer of diethyleneglycol bis (allyl carbonate).
 13. A photochromicarticle according to claim 10, wherein the amount of naphthopyrancompound is from 0.001 to 0.1% by weight, based on the weight of thepolymeric host material.
 14. A photochromic article according to claim10, comprising a further photochromic compound selected fromspiro(indoline) naphthoxazines, spiro(indolino)pyrido benzoxazines, andspiro(indolino)benzoxazines.
 15. A photochromic article according toclaim 14, wherein the further photochromic compound is present in anamount of from 0.001 to 0.5% by weight, based on the weight of thepolymeric host material.
 16. A photochromic article according to claim10, which is in the form of a lens.
 17. A photochromic article accordingto claim 16, wherein the lens is an ophthalmic lens.
 18. A naphthopyranselected from the group consisting of3,3-Dianisyl-6-piperidino-3H-naphtho[2,1-b] pyran,3,3-Dianisyl-6-morpholino-3H-naphtho[2,1-b]pyran,3-Anisyl-3-(p-trifluoromethylphenyl)-6-morpholino-3H-naphtho[2,1-b]pyran,3-Anisyl-3-(2,4-dimethoxyphenyl)-6-morpholino-3H-naphtho[2,1b]pyran, and1,3,3-Trimethyl-6'-morpholinosphiro[indoline-2,3'-(3H)-naphtho[2,1-b]pyran].
 19. The naphthopyran of claim 18 being3,3-Dianisyl-6-piperidino-3H -naphtho[2,1-b]pyran.
 20. The naphthopyranof claim 18 being 3,3-Dianisyl-6-morpholino-3H-naphtho[2,1-b]pyran. 21.The naphthopyran of claim 18 being3-Anisyl-3-(p-trifluoromethylphenyl)-6-morpholino-3H-naphtho[2,1-b]pyran.22. The naphthopyran of claim 18 being 3-Anisyl-3-(2,4-dimethoxyphenyl)-6-morpholino-3H-naphtho[2,1-b]pyran.
 23. The naphthopyran of claim 18being 1,3,3-Trimethyl-6'-morpholinosphiro[indoline-2,3'-[3H]-naphtho[2,1-b]pyran].